Some portable electronic devices comprise transducers such as loudspeakers and/or earpieces which are required to be small in size. Transducers are important components in electronic devices such as mobile phones for the purposes of playing back music or having a telephone conversation. The quality and loudness of a transducer in an electronic device are important especially if a user listens to sounds generated by an electronic device at a distance from the electronic device.
Furthermore in portable devices dust and water protection is important specifically with regards to the transducers. However dust and other small particles (and water) can often reach the transducer components and cause component damage. In particular the dynamic moving coil components in transducers radiate in each direction as the diaphragm moves forwards and backwards and as the construction of the transducer typically has open outlets on either side of the transducer which are free to air and the permanent magnet of a moving coil transducer can attract magnetic particles which migrate through the portable device and reach the coil and diaphragm. These particles can damage the sensitive components and/or reduce the performance of these components when the apparatus is in operation.
For example after some time the force between magnetic dust on the diaphragm and the permanent magnet inside the electrodynamic loudspeaker can pull the diaphragm towards the magnet and make the sound quieter, cause distortion or both. These types of failure typically requires repair and are costly to the manufacturer of the device if the failure occurs within the warranty period. Furthermore these features can cause brand damage if the failure occurs soon after the warranty period as the user considers the device to have failed prematurely and of poor quality.
Often a protective mesh or other porous material, where appropriate, is implemented to assist audio reproduction quality but maintain good reliability of the transducer by protecting the transducer from particles entering through the sound outlets in the device. For example a dust net can be placed in front of the loudspeaker. However the more effective a dust net is, in other words the denser the material used, the more attenuation to the sound generated by the speaker and therefore the muffling of the speaker output occurs.
In some situations a complicated mechanical channel structure can be used to improve dust protection by making the route longer from the outer surface of the phone to the loudspeaker diaphragm. However longer channel structures require additional volume within the device and furthermore require the height or depth of the phone to be increased in order to employ the additional channel length. These increased dimensions are counter to the current design trend to make the phone as thin as possible in order to create a device which is as portable as possible.
It has also been proposed that a permanent magnet can be used to collect the magnetic dust. However the employment of further permanent magnets not only increases the cost and that the number of parts required for the device but furthermore can increase stray magnetic fields which are detrimental to the use of the device as they can accidentally erase other magnetic items such as the magnetic strip on a credit card, debit card, a train ticket, or other device using a magnetic strip.
The use of magnetic shields have also been proposed (such as using a perforated μ-metal plate that lets sound pass through). The magnetic shield can be placed in front of the loudspeaker and used to weaken the stray magnetic field and effectively alter the direction of the attractive force. However in doing this it removes the ability of the loudspeaker to operate in a hearing aid compatibility (HAC) mode as typically hearing aid compatibility requires the coupling of magnetic fields such as those generated by the transducer.